Piezoelectric/electrostrictive device and method of manufacturing same

ABSTRACT

A piezoelectric/electrostrictive device includes a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section. One or more piezoelectric/electrostrictive elements are arranged on the pair of thin plate sections. A hole is formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section. At least one thin plate section of the pair of thin plate sections is previously bent in a direction to make mutual approach so that it has an inwardly convex configuration to the hole.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric/electrostrictive devicewhich is provided with a movable section to be operated on the basis ofa displacement action of a piezoelectric/electrostrictive element, or apiezoelectric/electrostrictive device which is capable of detectingdisplacement of a movable section by the aid of apiezoelectric/electrostrictive element, and a method for producing thesame. In particular, the present invention relates to apiezoelectric/electrostrictive device which is excellent in strength,shock resistance, and moisture resistance and which makes it possible toefficiently operate a movable section to a great extent, and a methodfor producing the same.

2. Background of the Invention

Recently, a displacement element, which makes it possible to adjust theoptical path length and the position in an order of submicron, isrequired, for example, in the fields of the optics, the magneticrecording, and the precision machining. Development is advanced for thedisplacement element based on the use of the displacement brought aboutby the inverse piezoelectric effect or the electrostrictive effectcaused when a voltage is applied to a piezoelectric/electrostrictivematerial (for example, a ferroelectric material).

As shown in FIG. 32, for example, those hitherto disclosed as such adisplacement element include a piezoelectric actuator comprising afixation section 204, a movable section 206, and a beam section 208 forsupporting them which are formed in an integrated manner with a hole 202provided through a plate-shaped member 200 composed of apiezoelectric/electrostrictive material and with an electrode layer 210provided on the beam section 208 (see, for example, Japanese Laid-OpenPatent Publication No. 10-136665).

The piezoelectric actuator is operated such that when a voltage isapplied to the electrode layer 210, the beam section 208 makes expansionand contraction in a direction along a line obtained by connecting thefixation section 204 and the movable section 206 in accordance with theinverse piezoelectric effect or the electrostrictive effect.

Therefore, the movable section 206 can perform circular arc-shapeddisplacement or rotational displacement in the plane of the plate-shapedmember 200.

On the other hand, Japanese Laid-Open Patent Publication No. 63-64640discloses a technique in relation to an actuator based on the use of abimorph. In this technique, electrodes for the bimorph are provided in adivided manner. The actuator is driven due to the selection of thedivided electrodes, and thus the highly accurate positioning isperformed at a high speed. This patent document discloses a structureespecially in FIG. 4 in which, for example, two bimorphs are used in anopposed manner.

However, the piezoelectric actuator described above involves such aproblem that the amount of operation of the movable section is small,because the displacement in the direction of extension and contractionof the piezoelectric/electrostrictlve material (i.e., in the in-planedirection of the plate-shaped member) is transmitted the movable sectionas it is.

All of the parts of the piezoelectric actuator are made of thepiezoelectric/electrostrictive material which is a fragile materialhaving a relatively heavy weight. Therefore, the following problemsarise. That is, the mechanical strength is low, and the piezoelectricactuator is inferior in handling performance, shock resistance, andmoisture resistance. Further, the piezoelectric actuator itself isheavy, and its operation tends to be affected by harmful vibrations (forexample, residual vibration and noise vibration during high speedoperation).

In order to solve the problems described above, it has been suggestedthat the hole is filled with a filler material having flexibility.However, it is clear that the amount of displacement, which is broughtabout by the inverse piezoelectric effect or the electrostrictiveeffect, is decreased even when the filler material is merely used.

On the other hand, the following structure is disclosed FIG. 4 inJapanese Laid-Open Patent Publication No. 63-64640. That is, in a joinedform between a mediating member and a bimorph and between a head and thebimorph, so-called piezoelectric operating sections, both of which causethe strain, extend over respective joined portions. In other words, thebimorph is formed continuously ranging from the mediating member to thehead.

As a result, when the bimorph is operated, the displacement action,which is effected with the supporting point of the joined portionbetween the mediating member and the bimorph, mutually interferes withthe displacement action which is effected with the supporting point ofthe joined point between the head and the bimorph. The expression of thedisplacement is inhibited. In this structure, it is impossible to obtainsuch a function that the head is greatly displaced with respect to theexternal space.

The conventional device of this type involves a problem that in order todisplace sufficiently the movable section, a large amount of voltagemust be applied.

SUMMARY OF THE INVENTION

The present invention has been made taking the foregoing problems intoconsideration, an object of which is to provide apiezoelectric/electrostrictive device and a method for producing thesame which make it possible to obtain a displacement element that isscarcely affected by harmful vibration during operation and capable ofhigh speed response with high mechanical strength while being excellentin handling performance, shock resistance, and moisture resistance,which is liable to cause the displacement in a specific axis directionand can increase the displacement amount of a movable section whilekeeping a voltage applied to a piezoelectric/electrostrictive element ata low level, as well as a sensor element that makes it possible todetect vibration of the movable section with good accuracy and highsensitivity.

According to the present invention, there is provided apiezoelectric/electrostrictive device comprising a pair of mutuallyopposing thin plate sections, a movable section, and a fixation sectionfor supporting the thin plate sections and the movable section; one ormore piezoelectric/electrostrictive elements arranged on at least onethin plate section of the pair of thin plate sections; and a hole formedby both inner walls of the pair of thin plate sections, an inner wall ofthe movable section, and an inner wall of the fixation section; whereinat least one thin plate section of the pair of thin plate sections ispreviously bent in a direction to make mutual approach.

According to another aspect of the present invention, there is provideda piezoelectric/electrostrictive device as described above, wherein thepair of thin plate sections are previously bent in directions to makemutual approach. In this arrangement, it is also preferable that atleast one thin plate section of the pair of thin plate sections, or thepair of thin plate sections are previously bent inwardly in convexconfigurations.

Usually, a thin plate section is bent as a voltage is applied to apiezoelectric/electrostrictive element, whereby a movable section causesdisplacement. In the present invention, since the pair of thin platesections are previously bent in directions to make mutual approach anddeformed in a direction substantially the same as bending directions ofthe thin plate sections due to the action of thepiezoelectric/electrostrictive element, the thin plate sections are bentby a relatively small force, whereby the movable section causesdisplacement. Namely, in the present invention, as compared with theconventional piezoelectric/electrostrictive devices, equivalentdisplacement (displacement in the movable section) can be obtained witha low voltage, whereby an electric power consumption of electronicinstruments installed with the piezoelectric/electrostrictive device canbe reduced.

Further, the structure in which the thin plate sections are previouslybent inwardly in convex configurations is a structure in which not onlya high resistance is exhibited against an external force from the widthdirection of the thin plate section, but also the structure itself isliable to cause displacement in a specific axis direction of eachmovable section, i.e., in a uniaxial direction along which each thinplate section opposes to the other. Accordingly, this structure has acharacteristic that the movable section is hardly rotated in an arc orrotational state, thereby making it possible to displace in an externalspace to a great extent.

It is preferable that 0<δ≦0.13 L is satisfied provided that a bentamount (previously bent amount) of the thin plate section is δ, and alength of the thin plate section (distance between the inner walls ofthe movable section and the fixation section) is L. When the bent amountis set to be within the range described above, the displacement of thepiezoelectric/electrostrictive element can be utilized as thedisplacement of the movable section more efficiently. As a result, themovable section can be displaced to a great extent.

The movable section, the fixation section, and the thin plate sectionmay be made of ceramics or metal. Alternatively, each of the componentsmay be made of a ceramic material, or each of them may be made of ametal material. Further, each of the components may be constructed tohave a hybrid structure obtained by combining those produced frommaterials of ceramics and metal.

In the arrangement described above, it is also preferable that the thinplate section, the movable section, and the fixation section arecomposed of a ceramic substrate integrated into one unit bysimultaneously sintering a ceramic green laminate and cutting offunnecessary portions. It is also preferable that thepiezoelectric/electrostrictive element has a film-shaped configuration,and at least any one of the pair of electrodes and/or apiezoelectric/electrostrictive layer is integrated with the ceramicsubstrate by means of sintering.

In this arrangement, the piezoelectric/electrostrictive element may havea piezoelectric/electrostrictive layer and a pair of electrodes formedon the piezoelectric/electrostrictive layer. It is also preferable thatthe piezoelectric/electrostrictive element has apiezoelectric/electrostrictive layer and a pair of electrodes formed onboth sides of the piezoelectric/electrostrictive layer, and oneelectrode of the pair of electrodes is formed on at least the thin platesection. In this arrangement, the vibration caused by thepiezoelectric/electrostrictive element can be efficiently transmittedvia the thin plate section to the movable section or the fixationsection. Thus, it is possible to improve the response performance.Especially, it is preferable that the piezoelectric/electrostrictiveelement is constructed in a stacked form comprising a plurality of thepiezoelectric/electrostrictive layers and the electrodes.

When the arrangement as described above is adopted, the followingfeature is achieved. That is, the generated force of thepiezoelectric/electrostrictive element is increased, and thus it ispossible to obtain large displacement. Further, it is possible to obtaina high resonance frequency owing to the increase in rigidity of thedevice itself, making it easy to achieve the high speed of thedisplacement action. Further, it is also preferable that the hole isfilled with a gel material.

According to still another aspect of the present invention, there isprovided a method for producing a piezoelectric/electrostrictive devicecomprising a pair of mutually opposing thin plate sections, a movablesection, and a fixation section for supporting the thin plate sectionsand the movable section; one or more piezoelectric/electrostrictiveelements arranged on at least one thin plate section of the pair of thinplate sections; and a hole formed by both inner walls of the pair ofthin plate sections, an inner wall of the movable section, and an innerwall of the fixation section; the method comprising the step of cuttingoff a predetermined portion after forming thepiezoelectric/electrostrictive element on at least the thin platesection to produce the piezoelectric/electrostrictive device in which atleast one thin plate section of the pair of thin plate sections is bentin a direction to make mutual approach.

According to still another aspect of the present invention, there isprovided a production method as described above, comprising the step ofcutting off a predetermined portion after forming thepiezoelectric/electrostrictive element on at least the thin platesection to produce the piezoelectric/electrostrictive device in whichthe pair of thin plate sections are previously bent in directions tomake mutual approach.

The phrase “after producing the piezoelectric/electrostrictive element”referred to herein indicates a state in which at least thepiezoelectric/electrostrictive layer is formed. As for the electrode tobe formed after the formation of the piezoelectric/electrostrictivelayer, the electrode may be formed after performing the cutoff.

According to still another aspect of the present invention, there isprovided a production method as described above, comprising the steps ofintegrally sintering a ceramic green laminate including at least a firstceramic green sheet having a window for forming at least the holethereafter and second ceramic green sheets to be formed into the thinplate sections thereafter to produce a ceramic laminate includingportions to be formed into the thin plate sections thereafter dentinginwardly; forming the piezoelectric/electrostrictive element on at leastan outer surface of a portion of the ceramic laminate to be formed intothe thin plate section; and producing a ceramic substrate formed with atleast the piezoelectric/electrostrictive element in which the pair ofthin plate sections are bent in directions to make mutual approach, bymeans of at least one time of cutoff treatment for the ceramic laminateformed with the piezoelectric/electrostrictive element. In this process,it is preferable that those having a difference in sintering shrinkagespeed and/or sintering shrinkage amount are used for the first andsecond ceramic green sheets respectively.

It is also preferable that the step of forming thepiezoelectric/electrostrictive element is performed in accordance with afilm formation method; and any one of a pair of electrodes and/or apiezoelectric/electrostrictive layer is integrated by sintering with atleast the outer surface of the portion to be formed into the thin platesection.

According to the production method described above, it is possible toproduce effectively and easily a piezoelectric/electrostrictive devicecapable of displacing a movable section to great extent while keeping avoltage of a piezoelectric/electrostrictive element at a low level.

Also, it is possible to mass-produce the piezoelectric/electrostrictivedevice having high performance.

According to still another aspect of the present invention, there isprovided a method for producing the piezoelectric/electrostrictivedevice as described above, comprising the steps of integrally sinteringa ceramic green laminate including at least a first ceramic green sheethaving a window for forming at least the hole thereafter and secondceramic green sheets to be formed into the thin plate sectionsthereafter to produce a ceramic laminate; forming a precursor of one ofa pair of electrodes constituting the piezoelectric/electrostrictiveelement and/or a piezoelectric/electrostrictive layer on at least anouter surface of a portion of the ceramic laminate to be formed into thethin plate section; sintering the precursor to integrate the ceramiclaminate with the precursor and simultaneously denting inwardly aportion to be formed into the thin plate section thereafter; andproducing a ceramic substrate formed with at least thepiezoelectric/electrostrictive element in which the pair of thin platesections are bent in directions to make mutual approach, by means of atleast one time of cutoff treatment for the ceramic laminate formed.

The step of forming the precursor of one of at least the pair ofelectrodes constituting the piezoelectric/electrostrictive elementand/or piezoelectric/electrostrictive layer may be carried out by a filmformation-method. In this case, it is preferable that the precursor isformed while controlling a difference in thermal expansion at leastbetween a material for the portion to be formed into the thin platesection and a material of precursor when the precursor is formed on theceramic laminate.

Accordingly, when the ceramic green laminate and the precursor aresintered, the portion to be formed into the thin plate sectionthereafter of the ceramic laminate is dented owing to the difference inthermal expansion at least between the material for the portion to beformed into the thin plate section and the material for the precursor,and the piezoelectric/electrostrictive element is consequently formed onthe portion to be formed into the thin plate section.

According to still another aspect of the present invention, there isprovided a method for producing the piezoelectric/electrostrictivedevice as described above, preferably comprising the steps of producinga ceramic green laminate including at least a ceramic green sheet havinga window for forming at least the hole thereafter and ceramic greensheets to be formed into the thin plate sections thereafter; forming aprecursor for constructing at least a part of thepiezoelectric/electrostrictive element on at least an outer surface of aportion to be formed into the thin plate section, of the ceramic greenlaminate; co-firing the ceramic green laminate and the precursor forconstructing at least the part or all of thepiezoelectric/electrostrictive element so that a ceramic laminateincluding portions to be formed into the thin plate sections thereafterdenting inwardly is produced, and at least the part or all of thepiezoelectric/electrostrictive element is formed on at least the outersurface of the portion to be formed into the thin plate section; andproducing a ceramic substrate in which the pair of thin plate sectionsare bent in directions to make mutual approach, by means of at least onetime of cutoff treatment for the ceramic laminate.

In this process, it is preferable that the precursor is formed whilecontrolling a difference in thermal expansion at least between amaterial for the portion to be formed into the thin plate section and amaterial for the precursor of the piezoelectric/electrostrictive elementwhen the precursor for constructing at least the part of thepiezoelectric/electrostrictive element is formed on the ceramic greenlaminate. Accordingly, when the ceramic green laminate and the precursorfor constructing at least the part or all of thepiezoelectric/electrostrictive element are sintered, then the portion tobe formed into the thin plate section thereafter of the ceramic laminateis dented owing to the difference in thermal expansion at least betweenthe material for the portion to be formed into the thin plate sectionand the material for the precursor for constructing at least the part ofthe piezoelectric/electrostrictive element, and thepiezoelectric/electrostrictive element is consequently formed on theportion to be formed into the thin plate section.

It is also preferable that the production methods described abovefurther comprise exposing the hole by means of a cutoff treatment forthe ceramic laminate in a combined manner.

Therefore, the piezoelectric/electrostrictive device according to thepresent invention can be utilized as the active device including, forexample, various transducers, various actuators, frequency regionfunctional parts (filters), transformers, vibrators, resonators,oscillators, and discriminators for the communication and the powergeneration, as well as the sensor element for various sensors including,for example, ultrasonic sensors, acceleration sensors, angular velocitysensors, shock sensors, and mass sensors. Especially, thepiezoelectric/electrostrictive device according to the present inventioncan be preferably utilized for various actuators to be used for themechanism for adjusting the displacement and the positioning and foradjusting the angle for various precision parts such as those of opticalinstruments and precision mechanical equipments.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to an embodiment of thepresent invention;

FIG. 2 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a first modifiedembodiment;

FIG. 3 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a second modifiedembodiment;

FIG. 4 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a third modifiedembodiment;

FIG. 5 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a fourth modifiedembodiment;

FIG. 6 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a fifth modifiedembodiment;

FIG. 7 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a sixth modifiedembodiment;

FIG. 8 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a seventh modifiedembodiment;

FIG. 9 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to an eighth modifiedembodiment;

FIG. 10 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a ninth modifiedembodiment;

FIG. 11 shows, with partial omission, another embodiment of thepiezoelectric/electrostrictive element;

FIG. 12 shows, with partial omission, still another embodiment of thepiezoelectric/electrostrictive element;

FIG. 13 illustrates a situation in which both of thepiezoelectric/electrostrictive elements do not make the displacementaction in the piezoelectric/electrostrictive device according to theembodiment of the present invention;

FIG. 14A shows a waveform illustrating a voltage waveform to be appliedto the first piezoelectric/electrostrictive element;

FIG. 14B shows a waveform illustrating a voltage waveform to be appliedto the second piezoelectric/electrostrictive element;

FIG. 15 illustrates a situation in which thepiezoelectric/electrostrictive element makes the displacement action inthe piezoelectric/electrostrictive device according to the embodiment ofthe present invention;

FIG. 16A illustrates a process for laminating necessary ceramic greensheets when the piezoelectric/electrostrictive device according to theembodiment of the present invention is produced in accordance with afirst production method;

FIG. 16B illustrates a state in which a ceramic green laminate isformed;

FIG. 16C illustrates a state in which the ceramic green laminate issintered to produce a ceramic laminate;

FIG. 17 illustrates a state in which the ceramic green laminate issintered into the ceramic laminate, and then apiezoelectric/electrostrictive element is formed on the ceramiclaminate;

FIG. 18 illustrates a state in which the ceramic laminate is cut alongpredetermined cutting lines to provide thepiezoelectric/electrostrictive device according to the embodiment of thepresent invention;

FIG. 19A illustrates a state in which a precursor of apiezoelectric/electrostrictive element is formed on a ceramic greenlaminate in a second production method;

FIG. 19B illustrates a state in which the ceramic green laminate and theprecursor of the piezoelectric/electrostrictive element are co-fired toform the piezoelectric/electrostrictive element on a ceramic laminate;

FIG. 20A illustrates a process in a third production method in which aprecursor of the piezoelectric/electrostrictive element is formed on theceramic laminate;

FIG. 20B illustrates a state in which the precursor of thepiezoelectric/electrostrictive element is sintered to form thepiezoelectric/electrostrictive element on the ceramic laminate;

FIG. 21A illustrates a process for laminating necessary ceramic greensheets when the piezoelectric/electrostrictive device according to atenth modified embodiment is produced in accordance with a fourthproduction method;

FIG. 21B illustrates a state in which a ceramic green laminate isformed;

FIG. 22A illustrates a state in which the ceramic green laminate issintered to produce a ceramic laminate;

FIG. 22B illustrates a state in which piezoelectric/electrostrictiveelements, which are constructed as other members, are bonded to surfacesof metal plates to serve as thin plate sections respectively;

FIG. 23 illustrates a state in the fourth production method in which themetal plates are bonded to the ceramic laminate to provide a hybridlaminate;

FIG. 24 illustrates a state in the fourth production method in which thehybrid laminate is cut along predetermined cutting lines to provide apiezoelectric/electrostrictive device according to the tenth modifiedembodiment;

FIG. 25A illustrates a state in which a ceramic green laminate issintered to produce a ceramic laminate in a fifth production method;

FIG. 25B illustrates a state in which the metal plates are bonded to theceramic laminate to provide a hybrid laminate;

FIG. 26 illustrates a state in the fifth production method in whichpiezoelectric/electrostrictive elements, which are constructed as othermembers, are bonded to surfaces of metal plates to serve as thin platesections respectively;

FIG. 27 illustrates a state in the fifth production method in which thehybrid laminate is cut along predetermined cutting lines to provide apiezoelectric/electrostrictive device according to an eleventh modifiedembodiment;

FIG. 28 shows a front view illustrating an arrangement of apiezoelectric/electrostrictive device according to a twelfth modifiedembodiment;

FIG. 29 shows a front view illustrating an arrangement of apiezoelectric/electrostrictive device according to a thirteenth modifiedembodiment;

FIG. 30 shows a front view illustrating an arrangement of apiezoelectric/electrostrictive device according to a fourteenth modifiedembodiment;

FIG. 31 shows a front view illustrating an arrangement of apiezoelectric/electrostrictive device according to a fifteenth modifiedembodiment; and

FIG. 32 shows an arrangement of a piezoelectric/electrostrictive deviceconcerning an illustrative conventional technique.

DETAILED DESCRIPTION OF THE INVENTION

Explanation will be made below with reference to FIGS. 1 to 31 forillustrative embodiments of the piezoelectric/electrostrictive deviceand the production method for the same according to the presentinvention.

It is noted that the piezoelectric/electrostrictive device resides in aconcept which includes the element for mutually converting the electricenergy and the mechanical energy by the aid of thepiezoelectric/electrostrictive element. Therefore, thepiezoelectric/electrostrictive device is most preferably used as theactive element such as various actuators and vibrators, especially asthe displacement element based on the use of the displacement broughtabout by the inverse piezoelectric effect or the electrostrictiveeffect. Additionally, the piezoelectric/electrostrictive device is alsopreferably used as the passive element such as acceleration sensorelements and shock sensor elements.

In this connection, the piezoelectric/electrostrictive device and thepiezoelectric/electrostrictive element mean a piezoelectric and/orelectrostrictive device and a piezoelectric and/or electrostrictiveelement, respectively.

As shown in FIG. 1, the piezoelectric/electrostrictive device 10according to this embodiment has a substrate 14 which has a lengthyrectangular parallelepiped-shaped configuration as a whole and which hasa hole 12 provided at an approximately central portion in the major axisdirection thereof.

The substrate 14 comprises a pair of mutually opposing thin platesections 16 a, 16 b, a movable section 20, and a fixation section 22 forsupporting the pair of thin plate sections 16 a, 16 b and the movablesection 20.

Piezoelectric/electrostrictive elements 24 a, 24 b are formed atrespective parts of at least the thin plate sections 16 a, 16 brespectively.

Those usable as the substrate 14 include a structure comprising ceramicsor metal as a whole, and a hybrid structure obtained by combiningproducts produced with materials of ceramics and metal.

Those adaptable for the substrate 14 include, for example, a structurein which respective parts are bonded to one another with an adhesivesuch as organic resin or glass or the like, a ceramic integratedstructure which is obtained by sintering and integrating a ceramic greenlaminate into one unit, and a metal integrated structure integrated bybrazing, soldering, eutectic bonding, or welding into one unit.Preferably, it is desirable to construct the substrate 14 with a ceramiclaminate integrated into one unit by sintering a ceramic green laminate.

The time-dependent change of state scarcely occurs in the integratedproduct of ceramic, because no adhesive exists at joined portionsbetween the respective parts. Therefore, the reliability of the joinedportion is high, giving a structure which is advantageous to ensure therigidity. Additionally, the integrated product of ceramic can beproduced with ease by means of the method for laminating ceramic greensheets as described later on.

The piezoelectric/electrostrictive elements 24 a, 24 b are prepared asseparate members as described later on, and the preparedpiezoelectric/electrostrictive elements 24 a, 24 b are affixed to thesubstrate 14 with an adhesive such as organic resin or glass or by meansof brazing, soldering, or eutectic bonding. Alternatively, thepiezoelectric/electrostrictive elements 24 a, 24 b are directly formedon the substrate 14 by using the film formation method not by using theadhesive method described above.

The piezoelectric/electrostrictive device 10 includes the hole 12having, for example, a rectangular configuration which is formed by bothinner walls of the pair of thin plate sections 16 a, 16 b, an inner wall20 a of the movable section 20, and an inner wall 22 a of the fixationsection 22. The piezoelectric/electrostrictive device 10 is constructedsuch that the movable section 20 is displaced in accordance with thedriving of the piezoelectric/electrostrictive element or elements 24 aand/or 24 b, or the displacement of the movable section 20 is detectedby the piezoelectric/electrostrictive element or elements 24 a and/or 24b.

Each of the piezoelectric/electrostrictive elements 24 a, 24 b comprisesa piezoelectric/electrostrictive layer 26, and a pair of electrodes 28,30 formed on both sides of the piezoelectric/electrostrictive layer 26.One electrode 28 of the pair of electrodes 28, 30 is formed at least oneach of the pair of thin plate sections 16 a, 16 b.

In the embodiment shown in FIG. 1, respective forward end surfaces ofthe pair of electrodes 28, 30 and the piezoelectric/electrostrictivelayer 26 for constructing the piezoelectric/electrostrictive elements 24a, 24 b are substantially aligned. A substantial driving portion 18 ofthe piezoelectric/electrostrictive elements 24 a, 24 b (portion at whichthe pair of electrodes 28, 30 are overlapped with each other with thepiezoelectric/electrostrictive layer 26 interposed therebetween) iscontinuously formed over a range from a part of the outercircumferential surface of the fixation section 22 to a part of theouter circumferential surface of the thin plate section 16 a, 16 b.Especially, in this embodiment, the respective forward end surfaces ofthe pair of electrodes 28, 30 are located at the positions slightlydeviated rearwardly from the inner wall 20 a of the movable section 20.Of course, the piezoelectric/electrostrictive elements 24 a, 24 b may beformed such that the substantial driving portion 18 is located over arange from a part of the movable section 20 to a part of the thin platesections 16 a, 16 b.

The voltage is applied to the pair of electrodes 28, 30 via terminals(pads) 32, 34 of the respective electrodes 28, 30 formed on the bothside surfaces (element formation surfaces) of the fixation section 22respectively. The respective terminals 32, 34 are positioned as follows.That is, the terminal 32 corresponding to the first electrode 28 isformed at the position deviated toward the rearward end of the fixationsection 22. The terminal 34 corresponding to the second electrode 30disposed on the side of the external space is formed at the positiondeviated toward the inner wall 22 a of the fixation section 22.

In this embodiment, the piezoelectric/electrostrictive device 10 can beindividually fixed by utilizing the surfaces respectively different fromthe surfaces on which the terminals 32, 34 are arranged. As a result, itis possible to obtain the high reliability for both of the fixation ofthe piezoelectric/electrostrictive device 10 and the electric connectionbetween the circuit and the terminals 32, 34. In this arrangement, theelectric connection between the terminals 32, 34 and the circuit ismade, for example, by means of the flexible print-circuit (also referredto as FPC), the flexible flat cable (also referred to as FFC), and thewire bonding.

Structures other than the structure shown in FIG. 1 are available forthe piezoelectric/electrostrictive elements 24 a, 24 b. That is, as in apiezoelectric/electrostrictive device 10 a according to a first modifiedembodiment shown in FIG. 2, it is also preferable that the respectiveforward ends of the pair of electrodes 28, 30 for constructing thepiezoelectric/electrostrictive elements 24 a, 24 b are aligned, and onlythe forward end of the piezoelectric/electrostrictive layer 26 isallowed to protrude toward the movable section 20. Alternatively, as ina piezoelectric/electrostrictive device 10 b according to a secondmodified embodiment shown in FIG. 3, it is also preferable that therespective forward ends of the first electrode 28 and thepiezoelectric/electrostrictive layer 26 are aligned, and only theforward end of the second electrode 30 is disposed at a positiondeviated toward the fixation section 22.

Alternatively, as in a piezoelectric/electrostrictive device 10 caccording to a third modified embodiment shown in FIG. 4, it is alsopreferable that the respective forward ends of the first electrode 28and the piezoelectric/electrostrictive layer 26 are allowed to extend upto the side surface of the movable section 20, and the forward end ofthe second electrode 30 is located at an approximately central portionin the length direction (Z axis direction) of the thin plate sections 16a, 16 b.

In the embodiments described above, the piezoelectric/electrostrictiveelements 24 a, 24 b are constructed by thepiezoelectric/electrostrictive layer 26 having the one-layered structureand the pair of electrodes 28, 30. Alternatively, it is also preferablethat the piezoelectric/electrostrictive elements 24 a, 24 b areconstructed in a stacked form composed of a plurality of thepiezoelectric/electrostrictive layer 26 and the electrodes 28, 30.

For example, as in a piezoelectric/electrostrictive device 10 daccording to a fourth modified embodiment shown in FIG. 5, each of thepiezoelectric/electrostrictive layer 26 and the pair of electrodes 28,30 resides in a multilayered structure. The first electrodes 28 and thesecond electrodes 30 are alternately stacked with each other to providethe piezoelectric/electrostrictive elements 24 a, 24 b which have amultiple stage structure at a portion (substantial driving portion 18)at which the first electrodes 28 and the second electrodes 30 areoverlapped with each other with the piezoelectric/electrostrictive layer26 interposed therebetween. FIG. 5 is illustrative of the followingcase. That is, the piezoelectric/electrostrictive layer 26 has thethree-layered structure. The first electrodes 28 are formed in aseparate manner respectively on the lower surface of the first layer(side surface of the thin plate sections 16 a, 16 b) and on the uppersurface of the second layer. The second electrodes 30 are formed in aseparate manner respectively on the upper surface of the first layer andon the upper surface of the third layer. Further, terminals 32 a, 32 bare provided on respective ends of the first electrodes 28 respectively,and terminals 34 a, 34 b are provided on respective ends of the secondelectrodes 30 respectively.

As in a piezoelectric/electrostrictive device 10 e according to a fifthmodified embodiment shown in FIG. 6, each of thepiezoelectric/electrostrictive layer 26 and the pair of electrodes 28,30 resides in a multilayered structure. The first electrode 28 and thesecond electrode 30 are alternately stacked with each other so that asubstantially comb-shaped configuration is obtained in cross section toprovide the piezoelectric/electrostrictive elements 24 a, 24 b whichhave a multiple stage structure at a portion (substantial drivingportion 18) at which the pair of electrode 28 and the second electrode30 are overlapped with each other with thepiezoelectric/electrostrictive layer 26 interposed therebetween. Theembodiment shown in FIG. 6 is illustrative of the following case. Thatis, the piezoelectric/electrostrictive layer 26 has the three-layeredstructure. The first electrode 28 is formed in a comb-shapedconfiguration to be located on the lower surface of the first layer(side surface of the thin plate sections 16 a, 16 b) and on the uppersurface of the second layer. The second electrode 30 is formed in acomb-shaped configuration to be located on the upper surface of thefirst layer and on the upper surface of the third layer. In the case ofthis structure, each of the first electrode 28 and the second electrode30 is continuous and common. Accordingly, it is possible to decrease thenumber of terminals 32, 34 as compared with the structure shown in FIG.5. Therefore, it is possible to suppress the increase in size whichwould be otherwise involved in the multilayered structure of thepiezoelectric/electrostrictive elements 24 a, 24 b.

As in a piezoelectric/electrostrictive device 10 f according to a sixthmodified embodiment is shown in FIG. 7, it is also preferable to formthe piezoelectric/electrostrictive elements 24 a, 24 b so that theforward end thereof stays on the thin plate sections 16 a, 16 b. FIG. 7is illustrative of a case in which the forward end of the firstelectrode 28 is located at a substantially central portion in the lengthdirection of the thin plate sections 16 a, 16 b. This arrangement isadvantageous in that the movable section 20 can be displaced to a greatextent.

As in a piezoelectric/electrostrictive device 10 g according to aseventh modified embodiment shown in FIG. 8, it is also preferable thatthe movable section 20 is provided with mutually opposing end surfaces36 a, 36 b. In this arrangement, the internal residual stress, which hasbeen generated in the piezoelectric/electrostrictive elements 24 a, 24 band/or the thin plate sections 16 a, 16 b during the production, can bereleased by the movement of the end surfaces 36 a, 36 b. Therefore, thedisplacement action of the movable section 20 is not inhibited by theinternal residual stress. Thus, it is possible to obtain thedisplacement action of the movable section 20 as designed substantiallyexactly. Additionally, owing to the release of the stress, it is alsopossible to improve the mechanical strength of thepiezoelectric/electrostrictive device 10 g.

As shown in FIG. 8, a gap (air) 38 may be allowed to intervene betweenthe end surfaces 36 a, 36 b. Alternatively, a member different from theconstitutive member of the movable section 20, for example, a member 40composed of, for example, resin or the like may be allowed to intervenebetween the end surfaces 36 a, 36 b. The embodiment described above isillustrative of the case in which the mutually opposing end surfaces 36a, 36 b are provided on the movable section 20. Alternatively, themutually opposing end surfaces 36 a, 36 b may be provided on thefixation section 22.

Alternatively, as in a piezoelectric/electrostrictive device 10 haccording to an eighth modified embodiment shown in FIG. 9, it is alsopreferable that two piezoelectric/electrostrictive elements 24 a 1, 24 b1 having the multiple stage structure are formed to extend over thefixation section 22 and the thin plate sections 16 a, 16 b,respectively, and another two piezoelectric/electrostrictive elements 24a 2, 24 b 2 having the multiple stage structure are formed to extendover the movable section 20 and the thin plate sections 16 a, 16 b,respectively. In this arrangement, the movable section 20 can bedisplaced extremely greatly owing to the effect that thepiezoelectric/electrostrictive elements 24 a, 24 b have the multiplestage structure and the effect that the number of points of action todisplace the movable section 20 is increased. Additionally, thepiezoelectric/electrostrictive device 10 h is excellent in high speedresponse performance, which is preferred.

Alternatively, as in a piezoelectric/electrostrictive device 10 iaccording to a ninth modified embodiment shown in FIG. 10, it is alsopreferable that the piezoelectric/electrostrictive layer 26 has thetwo-layered structure to provide the piezoelectric/electrostrictiveelements having the multiple stage structure which are formed in acomb-shaped configuration such that the first electrode 28 is located onthe lower surface of the first layer (side surface of the thin platesections 16 a, 16 b) and on the upper surface of the second layer, andthe second electrode 30 is located on the upper surface of the firstlayer.

The multiple stage structure of the piezoelectric/electrostrictiveelements 24 a, 24 b as described above increases the force generated bythe piezoelectric/electrostrictive elements 24 a, 24 b, and thus it ispossible to obtain the large displacement. Further, the rigidity of thepiezoelectric/electrostrictive device 10 itself is increased, and thusit is possible to realize the high resonance frequency. It is possibleto achieve the high speed displacement action with ease.

The frequency as referred to herein means a frequency of voltagewaveform when the voltage applied to a pair of electrodes 28, 30 isalternately switched to displace the movable section 20 right and left;and the resonance frequency as referred to herein means a maximumfrequency at which the displacement action of the movable section 20 canfollow in a predetermined vibration mode.

When the number of stages of the piezoelectric/electrostrictive elements24 a, 24 b is increased, it is possible to increase the driving force.However, the electric power consumption is also increased in accordancetherewith. Therefore, when the device is practically produced and used,for example, it is preferable that the number of stages is appropriatelydetermined depending on the way of use and the state of use. In the caseof the piezoelectric/electrostrictive device 10 according to thisembodiment, even when the driving force is increased by providing themultiple stage structure of the piezoelectric/electrostrictive elements24 a, 24 b, the width of the thin plate sections 16 a, 16 b (distance inthe Y axis direction) is basically unchanged. Therefore, the device isextremely preferred to make application, for example, to the actuatorfor the purpose of the ringing control and the positioning of themagnetic head for the hard disk drive to be used in an extremely narrowgap.

The piezoelectric/electrostrictive elements 24 a, 24 b are illustrativeof the case of the so-called sandwich structure in which thepiezoelectric/electrostrictive layer 26 is interposed between the pairof electrodes 28, 30. Alternatively, as shown in FIG. 11, a pair ofelectrodes 28, 30 having the comb-shaped structure may be formed on thefirst principal surface of the piezoelectric/electrostrictive layer 26formed on at least the side surface of the thin plate sections 16 a, 16b. Further alternatively, as shown in FIG. 12, a pair of electrodes 28,30 having the comb-shaped structure may be formed and embedded in thepiezoelectric/electrostrictive layer 26 formed on at least the sidesurface of the thin plate sections 16 a, 16 b.

The structure shown in FIG. 11 is advantageous in that it is possible tosuppress the electric power consumption to be low. The structure shownin FIG. 12 makes it possible to effectively utilize the inversepiezoelectric effect in the direction of the electric field having largegenerated force and strain, which is advantageous to cause the largedisplacement.

Specifically, the piezoelectric/electrostrictive elements 24 a, 24 bshown in FIG. 11 comprise the pair of electrodes 28, 30 having thecomb-shaped structure formed on the first principal surface of thepiezoelectric/electrostrictive layer 26. In this structure, the firstelectrode 28 and the second electrode 30 are mutually opposed to oneanother in an alternate manner with a gap 29 having a constant widthinterposed therebetween. FIG. 11 is illustrative of the case in whichthe pair of electrodes 28, 30 are formed on the first principal surfaceof the piezoelectric/electrostrictive layer 26. Alternatively, the pairof electrodes 28, 30 may be formed between the thin plate sections 16 a,16 b and the piezoelectric/electrostrictive layer 26. Furtheralternatively, the pair of electrodes 28, 30 having the comb-shapedstructure may be formed on the first principal surface of thepiezoelectric/electrostrictive layer 26 and between the thin platesections 16 a, 16 b and the piezoelectric/electrostrictive layer 26respectively.

On the other hand, in the piezoelectric/electrostrictive elements 24 a,24 b shown in FIG. 12, the pair of electrodes 28, 30 having thecomb-shaped structure are formed so that they are embedded in thepiezoelectric/electrostrictive layer 26. In this structure, the firstelectrode 28 and the second electrode 30 are mutually opposed to oneanother in an alternate manner with a gap 29 having a constant widthinterposed therebetween.

The piezoelectric/electrostrictive elements 24 a, 24 b as shown in FIGS.11 and 12 can be preferably used for the piezoelectric/electrostrictivedevice 10 according to the embodiment of the present invention as well.When the pair of electrodes 28, 30 having the comb-shaped structure areused as in the piezoelectric/electrostrictive elements 24 a, 24 b shownin FIGS. 11 and 12, the displacement of thepiezoelectric/electrostrictive elements 24 a, 24 b can be increased bydecreasing the pitch D of the comb teeth of the respective electrodes28, 30.

As shown in FIG. 1, the piezoelectric/electrostrictive device 10according to this embodiment has such a structure that the pair of thinplate sections 16 a, 16 b are previously bent in directions to makeapproach from each other, and they are bent inwardly to the hole 12 in aconvex configuration. In this arrangement, as shown in FIG. 13, it isset that 0<δ≦0.13 L is satisfied provided that the bent amount(previously bent amount) of each of the thin plate sections 16 a, 16 bis δ, and the length of the thin plate sections 16 a, 16 b (distancebetween the inner walls 20 a, 22 a of the movable section 20 and thefixation section 22) is L. If the bent amount δ exceeds 0.13 L, therigidity of the thin plate sections 16 a, 16 b is extremely reduced,which is disadvantageous. Further, if the bent amount δ exceeds 0.13 L,the displacement of the movable section 20 is liable to draw an arc-liketrace, whereby the displacement to a specific axis as described below ishardly obtained. The term “previously” referred to herein indicates astate in which no voltage is applied to thepiezoelectric/electrostrictive elements 24 a, 24 b, or a state in whichno external force is applied to the piezoelectric/electrostrictivedevice 10, i.e., a non-operating state.

The operation of the piezoelectric/electrostrictive device 10 accordingto the embodiment of the present invention will now be explained. Atfirst, for example, when the two piezoelectric/electrostrictive elements24 a, 24 b are in the natural state, namely when both of thepiezoelectric/electrostrictive elements 24 a, 24 b do not make thedisplacement action, then the major axis m of thepiezoelectric/electrostrictive device 10 (major axis of the fixationsection) is substantially coincident with the central axis n of themovable section 20 as shown in FIG. 13.

Starting from this state, for example, a sine wave Wa, which has apredetermined bias electric potential Vb, is applied to the pair ofelectrodes 28, 30 of the first piezoelectric/electrostrictive element 24a as shown in a waveform figure shown in FIG. 14A, while a sine wave Wb,which has a phase different from that of the sine wave Wa by about 180°,is applied to the pair of electrodes 28, 30 of the secondpiezoelectric/electrostrictive element 24 b as shown in FIG. 14B.

The piezoelectric/electrostrictive layer 26 of the firstpiezoelectric/electrostrictive element 24 a makes the contractiondisplacement in the direction of the first principal surface at a stageat which, for example, a voltage having a maximum value is applied tothe pair of electrodes 28, 30 of the firstpiezoelectric/electrostrictive element 24 a. Accordingly, as shown inFIG. 15, for example, the stress is generated for the first thin platesection 16 a to bend the thin plate section 16 a, for example, in therightward direction as shown by the arrow A. Therefore, the first thinplate section 16 a is bent in the rightward direction. At this time, astate is given, in which no voltage is applied to the pair of electrodes28, 30 of the second piezoelectric/electrostrictive element 24 b.Therefore, the second thin plate section 16 b follows the bending of thefirst thin plate section 16 a, and it is bent in the rightwarddirection. As a result, the movable section 20 is displaced, forexample, in the rightward direction with respect to the major axis m ofthe piezoelectric/electrostrictive device 10. The displacement amount ischanged depending on the maximum value of the voltage applied to each ofthe piezoelectric/electrostrictive elements 24 a, 24 b. For example, thelarger the maximum value is, the larger the displacement amount is.

Especially, when a material having coercive electric field is applied asthe constitutive material for the piezoelectric/electrostrictive layer26, it is also preferable that the bias electric potential is adjustedso that the level of the minimum value is a slightly negative level asdepicted by waveforms indicated by dashed lines in FIGS. 14A and 14B. Inthis case, for example, the stress, which is in the same direction asthe bending direction of the first thin plate section 16 a, is generatedin the second thin plate section 16 b by driving thepiezoelectric/electrostrictive element (for example, the secondpiezoelectric/electrostrictive element 24 b) to which the negative levelis applied. Accordingly, it is possible to further increase thedisplacement amount of the movable section 20. In other words, when thewaveforms indicated by the chain double-dashed lines in FIGS. 14A and14B are used, the device is allowed to have such a function that thepiezoelectric/electrostrictive element 24 b or 24 a, to which thenegative level is applied, supports the piezoelectric/electrostrictiveelement 24 a or 24 b which principally makes the displacement action.

In the piezoelectric/electrostrictive 10 according to this embodiment,since the thin plate sections 16 a, 16 b are previously bent indirections to make mutual approach and deformed in a directionsubstantially same as bending directions of the thin plate sections 16a, 16 b due to the action of the piezoelectric/electrostrictive elements24 a, 24 b, the thin plate sections 16 a, 16 b are bent by a relativelysmall force, whereby the movable section 20 causes displacement. Namely,in this embodiment, as compared with the conventionalpiezoelectric/electrostrictive devices, equivalent displacement(displacement in the movable section 20) can be obtained with a lowvoltage, whereby an electric power consumption of electronic instrumentsinstalled with the piezoelectric/electrostrictive device 10 can bereduced.

In addition, the structure in which the pair of the thin plate sections16 a, 16 b are previously bent in directions to make mutual approach isalso a structure in which, from the viewpoint of the bending action ofthe second thin plate section 16 b bending following the bending of thethin plate section 16 a due to the action of the firstpiezoelectric/electrostrictive element 24 a, the second thin platesection 16 b is previously bent in a direction where the movable section20 causes displacement due to the action of the firstpiezoelectric/electrostrictive element 24 a.

In other words, the explanation is made with reference to FIG. 15. Sincethe second thin plate section 16 b is previously bent to a directionsame as the direction as shown by the arrow A, the second thin platesection 16 b is liable to cause displacement in the axis direction wherethe pair of the thin plate sections 16 a, 16 b are opposed. Accordingly,the movable section 20 causes the displacement hardly in an arc orrotational state but rather in a uniaxial direction. As a result, it ispossible to displace the movable section 20 toward the external space toa great extent.

In the case of the piezoelectric/electrostrictive device 10 h accordingto the eighth embodiment shown in FIG. 9, the voltage (see the sinewaveform Wa) shown in FIG. 14A is applied, for example, to thepiezoelectric/electrostrictive element 24 a 1 and thepiezoelectric/electrostrictive element 24 b 2 which are arranged on thediagonal line, and the voltage (see the sine waveform Wb) shown in FIG.14B is applied to the other piezoelectric/electrostrictive element 24 a2 and the other piezoelectric/electrostrictive element 24 b 1.

As described above, in the piezoelectric/electrostrictive device 10according to the embodiment of the present invention, the minutedisplacement of the piezoelectric/electrostrictive elements 24 a, 24 bis amplified into the large displacement action by utilizing the bendingof the thin plate sections 16 a, 16 b, and it is transmitted to themovable section 20. Accordingly, it is possible to greatly displace themovable section 20 with respect to the major axis m of thepiezoelectric/electrostrictive device 10.

In the piezoelectric/electrostrictive device 10 according to thisembodiment, the movable section 20, the thin plate sections 16 a, 16 b,and the fixation section 22 are integrated into one unit. It isunnecessary that all of the parts are formed with thepiezoelectric/electrostrictive material which is a fragile materialhaving a relatively heavy weight. Therefore, the device has thefollowing advantages. That is, the device has the high mechanicalstrength, and it is excellent in handling performance, shock resistance,and moisture resistance. Further, the operation of the device isscarcely affected by harmful vibration (for example, noise vibration andremaining vibration during high speed operation).

In this embodiment, the piezoelectric/electrostrictive elements 24 a, 24b are constructed to have the piezoelectric/electrostrictive layer 26and the pair of electrodes 28, 30 formed on the both sides of thepiezoelectric/electrostrictive layer 26. The first electrode 28 of thepair of electrodes 28, 30 is formed on at least the outer surface of thethin plate sections 16 a, 16 b. Therefore, the vibration caused by thepiezoelectric/electrostrictive elements 24 a, 24 b can be efficientlytransmitted to the movable section 20 via the thin plate sections 16 a,16 b. Thus, it is possible to improve the response performance.

In this embodiment, the portion (substantial driving portion 18), atwhich the pair of electrodes 28, 30 are overlapped with each other withthe piezoelectric/electrostrictive layer 26 interposed therebetween, iscontinuously formed over the range from the part of the fixation section22 to the part of the thin plate sections 16 a, 16 b. If the substantialdriving portion 18 is formed to further extend over a part of themovable section 20, then it is feared that the displacement action ofthe movable section 20 is restricted by the substantial driving portion18, and it is impossible to obtain the large displacement. However, inthis embodiment, the substantial driving portion 18 is formed such thatit does not range over both of the movable section 20 and the fixationsection 22. Therefore, it is possible to avoid the inconvenience of therestriction of the displacement action of the movable section 20, and itis possible to increase the displacement amount of the movable section20, owing to the synergistic effect combined with the effect that thethin plate sections 16 a, 16 b are previously bent in the directions tomake separation from each other as described above.

On the other hand, when the piezoelectric/electrostrictive elements 24a, 24 b are formed on the part of the movable section 20, it ispreferable that the substantial driving portion 18 is located over therange from the part of the movable section 20 to the part of the thinplate sections 16 a, 16 b, because of the following reason. That is, ifthe substantial driving portion 18 is formed to extend up to a part ofthe fixation section 22, the displacement action of the movable section20 is restricted as described above.

Next, explanation will be made for preferred illustrative constructionsof the piezoelectric/electrostrictive device 10 according to theembodiment of the present invention.

At first, as shown in FIG. 1, in order to ensure the displacement actionof the movable section 20, it is preferable that the distance g, bywhich the substantial driving portion 18 of thepiezoelectric/electrostrictive elements 24 a, 24 b is overlapped withthe fixation section 22 or the movable section 20, is not less than ½ ofthe thickness d of the thin plate sections 16 a, 16 b.

The device is constructed such that the ratio a/b between the distance aselected as a larger distance from the distance in the X axis directionbetween the joined portions of the inner wall 20 a of the movablesection 20 and the thin plate sections 16 a, 16 b and the distance inthe X axis direction between the joined portions of the inner wall 22 aof the fixation section 22 and the thin plate sections 16 a, 16 b, andthe width (distance in the Y axis direction) b of the thin platesections 16 a, 16 b is 0.5 to 20. The ratio a/b is preferably 1 to 10and more preferably 2 to 8. The prescribed value of the ratio a/b isprescribed on the basis of the discovery that the displacement amount ofthe movable section 20 can be increased, and the displacement in the X-Zplane can be dominantly obtained.

On the other hand, it is desirable that the ratio L/a between the length(distance in the Z axis direction) L of the thin plate sections 16 a, 16b and the distance a described above is preferably 0.5 to 10 and morepreferably 0.7 to 5. The prescribed value of the ratio L/a is prescribedon the basis of the discovery that the displacement amount of themovable section 20 can be increased, and the displacement action can beperformed at a high resonance frequency (high response speed can beachieved).

Therefore, in order to suppress the flapping displacement in the Y axisdirection or the vibration of the piezoelectric/electrostrictive device10 according to this embodiment and provide the structure in which thehigh speed response performance is excellent and the large displacementis simultaneously obtained at a relatively low voltage, it is preferablethat the ratio a/b is 0.5 to 20 and the ratio L/a is 0.5 to 10, and itis more preferable that the ratio a/b is 1 to 10 and the ratio L/a is0.7 to 5.

Further, it is preferable that the hole 12 is filled with a gelmaterial, for example, silicone gel. Usually, the displacement action ofthe movable section 20 is restricted by the presence of such a fillermaterial. However, in this embodiment, it is intended to increase thedisplacement amount of the movable section 20 by bending the thin platesections 16 a, 16 b in directions to make mutual approach. Therefore,the restriction of the displacement action of the movable section 20 dueto the filler material is counteracted. Accordingly, it is possible torealize the effect owing to the presence of the filler material, namelythe realization of the high resonance frequency and the maintenance ofthe rigidity.

It is preferable that the length (distance in the Z axis direction) f ofthe movable section 20 is short, because of the following reason. Thatis, it is possible to realize the light weight and increase theresonance frequency by shortening the length. However, in order toensure the rigidity of the movable section 20 in the X axis directionand obtain its reliable displacement, it is desirable that the radio f/dwith respect to the thickness d of the thin plate sections 16 a, 16 b isnot less than 3 and preferably not less than 10.

The actual size of each component is determined considering, forexample, the joining area for attaching the part to the movable section20, the joining area for attaching the fixation section 22 to anothermember, the joining area for attaching the electrode terminal or thelike, and the strength, the durability, the necessary displacementamount, the resonance frequency, and the driving voltage of the entirepiezoelectric/electrostrictive device 10.

Specifically, for example, the distance a selected as the largerdistance from the distance in the X axis direction between the joinedportions of the inner wall 20 a of the movable section 20 and the thinplate sections 16 a, 16 b and the distance in the X axis directionbetween the joined portions of the inner wall 22 a of the fixationsection 22 and the thin plate sections 16 a, 16 b is preferably 100 μmto 2000 μm and more preferably 200 μm to 1000 μm. The width b of thethin plate sections 16 a, 16 b is preferably 50 μm to 2000 μm and morepreferably 100 μm to 500 μm. The thickness d of the thin plate sections16 a, 16 b is preferably 2 μm to 100 μm and more preferably 4 μm to 50μm, while it satisfies b>d in relation to the width b of the thin platesections 16 a, 16 b, in order to make it possible to effectivelysuppress the flapping displacement which is the displacement componentin the Y axis direction.

The length L of the thin plate sections 16 a, 16 b is preferably 200 μmto 3000 μm and more preferably 300 μm to 2000 μm. The length f of themovable section 20 is preferably 50 μm to 2000 μm and more preferably100 μm to 1000 μm.

The arrangement as described above exhibits such an extremely excellenteffect that the displacement in the Y axis direction does not exceeds10% with respect to the displacement in the X axis direction, while thedevice can be driven at a low voltage by appropriately making adjustmentwithin the range of the size ratio and the actual size described above,and it is possible to suppress the displacement component in the Y axisdirection to be not more than 5%. In other words, the movable section 20is displaced in one axis direction, i.e., substantially in the X axisdirection. Further, the high speed response is excellent, and it ispossible to obtain the large displacement at a relatively low voltage.

In the piezoelectric/electrostrictive device 10, the shape of thepiezoelectric/electrostrictive device is not the plate-shapedconfiguration unlike conventional one. Each of the movable section 20and the fixation section 22 has the rectangular parallelepiped-shapedconfiguration. The pair of thin plate sections 16 a, 16 b are providedso that the side surface of the movable section 20 is continuous to theside surface of the fixation section 22. Additionally, the pair of thinplate sections 16 a, 16 b are previously bent in the directions to makemutual approach. Therefore, it is possible to selectively increase therigidity of piezoelectric/electrostrictive device 10 in the Y axisdirection.

That is, in the piezoelectric/electrostrictive device 10, it is possibleto highly selectively generate only the operation of the movable section20 in the plane (XZ plane). It is possible to suppress the operation ofthe movable section 20 in the YZ plane (operation in the so-calledflapping direction).

Next, explanation will be made for the respective constitutivecomponents of the piezoelectric/electrostrictive device 10 according tothe embodiment of the present invention.

As described above, the movable section 20 is the portion which isoperated on the basis of the driving amount of the thin plate sections16 a, 16 b, and a variety of members are attached thereto depending onthe purpose of use of the piezoelectric/electrostrictive device 10. Forexample, when the piezoelectric/electrostrictive device 10 is used as adisplacement element, a shield plate for an optical shutter or the likeis attached thereto. Especially, when the piezoelectric/electrostrictivedevice 10 is used for the mechanism for positioning a magnetic head of ahard disk drive or for suppressing the ringing, a member required to bepositioned is attached thereto, including, for example, the magnetichead, a slider provided with the magnetic head, and a suspensionprovided with the slider.

As described above, the fixation section 22 is the portion forsupporting the thin plate sections 16 a, 16 b and the movable section20. For example, when the piezoelectric/electrostrictive device 10 isutilized to position the magnetic head of the hard disk drive, theentire piezoelectric/electrostrictive device 10 is fixed by supportingand securing the fixation section 22, for example, to a carriage armattached to VCM (voice coil motor) or a fixation plate or a suspensionattached to the carriage arm. As shown in FIG. 1, the terminals 32, 34for driving the piezoelectric/electrostrictive elements 24 a, 24 b andother members are arranged on the fixation section 22 in some cases.

The material for constructing the movable section 20 and the fixationsection 22 is not specifically limited provided that it has rigidity.However, it is possible to preferably use ceramics to which the ceramicgreen sheet-laminating method is applicable as described later on.Specifically, the material includes, for example, materials containing amajor component of zirconia represented by fully stabilized zirconia andpartially stabilized zirconia, alumina, magnesia, silicon nitride,aluminum nitride, and titanium oxide, as well as materials containing amajor component of a mixture of them. However, in view of the highmechanical strength and the high toughness, it is preferable to use amaterial containing a major component of zirconia, especially fullystabilized zirconia and a material containing a major component ofpartially stabilized zirconia. The metal material is not limitedprovided that it has rigidity. However, the metal material includes, forexample, stainless steel and nickel.

As described above, the thin plate sections 16 a, 16 b are the portionswhich are driven in accordance with the displacement of thepiezoelectric/electrostrictive elements 24 a, 24 b. The thin platesections 16 a, 16 b are the thin plate-shaped member having flexibility,and they function to amplify the expansion and contracting displacementof the piezoelectric/electrostrictive elements 24 a, 24 b arranged onthe surface as the bending displacement and transmit the, displacementto the movable section 20. Therefore, it is enough that the shape or thematerial of the thin plate sections 16 a, 16 b provides the flexibilitywith the mechanical strength of such a degree that it is not broken bythe bending displacement. It is possible to make appropriate selectionconsidering the response performance and the operability of the movablesection 20.

It is preferable that the thickness d of the thin plate sections 16 a,16 b is preferably about 2 μm to 100 μm. It is preferable that thecombined thickness of the thin plate section 16 a (or 16 b) and thepiezoelectric/electrostrictive element 24 a (or 24 b) is 7 μm to 500 μm.It is preferable that the thickness of the electrodes 28, 30 is 0.1 to50 μm, and the thickness of the piezoelectric/electrostrictive layer 26is 3 to 300 μm. The width b of the thin plate sections 16 a, 16 b ispreferably 50 μm to 2000 μm.

Ceramics, which is similarly used for the movable section 20 and thefixation section 22, can be preferably used as the material forconstructing the thin plate sections 16 a, 16 b. A material containing amajor component of zirconia, especially fully stabilized zirconia and amaterial containing a major component of partially stabilized zirconiaare most preferably used, because the mechanical strength is large evenin the case of a thin wall thickness, the toughness is high, and thereactivity with the piezoelectric/electrostrictive layer and theelectrode material is small.

When the thin plate sections 16 a, 16 b are made of a metal material, itis enough that the metal material has flexibility and the metal materialis capable of bending displacement as described above. However,preferably, it is desirable that the thin plate sections 16 a, 16 b aremade of an iron-based material such as various stainless steel materialsand various spring steel materials. Alternatively, it is desirable thatthe thin plate sections 16 a, 16 b are made of a non-ferrous materialsuch as beryllium copper, phosphor bronze, nickel, and nickel-ironalloy.

Those which are fully stabilized or partially stabilized as follows arepreferably used as fully stabilized zirconia or partially stabilizedzirconia as described above. That is, the compound to be used for fullystabilizing or partially stabilizing zirconia includes yttrium oxide,ytterbium oxide, cerium oxide, calcium oxide, and magnesium oxide. Whenat least one compound of them is added and contained, zirconia ispartially or fully stabilized. However, as for the stabilization, theobjective zirconia can be stabilized not only by adding one type of thecompound but also by adding a combination of the compounds.

The amount of addition of each of the compounds is desirably as follows.That is, yttrium oxide or ytterbium oxide is added by 1 to 30 mole %,preferably 1.5 to 10 mole %. Cerium oxide is added by 6 to 50 mole %,preferably 8 to 20 mole %. Calcium oxide or magnesium oxide is added by5 to 40 mole %, preferably 5 to 20 mole %. Especially, it is preferableto use yttrium oxide as a stabilizer. In this case, yttrium oxide isdesirably added by 1.5 to 10 mole %, more preferably 2 to 4 mole %. Forexample, alumina, silica, or transition metal oxide may be added as anadditive of sintering aid or the like in a range of 0.05 to 20% byweight. However, when the sintering integration based on the filmformation method is adopted as a technique for forming thepiezoelectric/electrostrictive elements 24 a, 24 b, it is alsopreferable to add, for example, alumina, magnesia, and transition metaloxide as an additive.

In order to obtain the mechanical strength and the stable crystal phase,it is desirable that the average crystal grain size of zirconia is 0.05to 3 μm, preferably 0.05 to 1 μm. As described above, ceramics can beused for the thin plate sections 16 a, 16 b in the same manner as in themovable section 20 and the fixation section 22.

Preferably, it is advantageous to construct the thin plate sections 16a, 16 b with a substantially identical material in view of thereliability of the joined portion and the strength of thepiezoelectric/electrostrictive device 10, in order to reduce anycomplicated procedure of the production.

The piezoelectric/electrostrictive elements 24 a, 24 b have at least thepiezoelectric/electrostrictive layer 26 and the pair of electrodes 28,30 for applying the electric field to the piezoelectric/electrostrictivelayer 26. It is possible to use, for example,piezoelectric/electrostrictive elements of the unimorph type and thebimorph type. However, those of the unimorph type are suitable for thepiezoelectric/electrostrictive device 10 as described above, becausethey are excellent in stability of the generated displacement amount andthey are advantageous to realize the light weight.

For example, as shown in FIG. 1, it is possible to preferably use, forexample, the piezoelectric/electrostrictive elements 24 a, 24 bcomprising the first electrode 28, the piezoelectric/electrostrictivelayer 26, and the second electrode 30 which are stacked in the layeredconfiguration. Additionally, it is also preferable to provide themultiple stage structure as shown in FIGS. 5 to 10.

As shown in FIG. 1, the piezoelectric/electrostrictive elements 24 a, 24b are preferably formed on the outer surface side of thepiezoelectric/electrostrictive device 10 in view of the fact that thethin plate-sections 16 a, 16 b can be driven to a greater extent.However, the piezoelectric/electrostrictive elements 24 a, 24 b may beformed on the inner surface side of the piezoelectric/electrostrictivedevice 10, i.e., on the inner wall surface of the hole 12 depending on,for example, the form of use. Alternatively, thepiezoelectric/electrostrictive elements 24 a, 24 b may be formed both onthe outer surface side and on the inner surface side.

Piezoelectric ceramics is preferably used for thepiezoelectric/electrostrictive layer 26. However, it is also possible touse electrostrictive ceramics, ferroelectric ceramics, oranti-ferroelectric ceramics. However, when thepiezoelectric/electrostrictive device 10 is used, for example, toposition the magnetic head of the hard disk drive, it is important toprovide the linearity concerning the displacement amount of the movablesection 20 and the driving voltage or the output voltage. Therefore, itis preferable to use a material having small strain hysteresis. It ispreferable to use a material having a coercive electric field of notmore than 10 kV/mm.

Specified materials include ceramics containing, for example, leadzirconate, lead titanate, lead magnesium niobate, lead nickel niobate,lead zinc niobate, lead manganese niobate, lead antimony stannate, leadmanganese tungstate, lead cobalt niobate, barium titanate, sodiumbismuth titanate, potassium sodium niobate, and strontium bismuthtantalate singly or in mixture, or in the form of a compound.

Especially, a material containing a major component of lead zirconate,lead titanate, and lead magnesium niobate, or a material containing amajor component of sodium bismuth titanate is preferably used, in orderto obtain the product having a stable composition with a highelectromechanical coupling factor and a piezoelectric constant and withsmall reactivity with the thin plate sections 16 a, 16 b (ceramics)during the sintering of the piezoelectric/electrostrictive layer 26.

It is also preferable to use ceramics obtained by adding, to thematerial described above, for example, oxides of lanthanum, calcium,strontium, molybdenum, tungsten, barium, niobium, zinc, nickel,manganese, cerium, cadmium, chromium, cobalt, antimony, iron, yttrium,tantalum, lithium, bismuth, and stannum singly or in mixture or incompound.

For example, when lanthanum and/or strontium is contained in the majorcomponents of lead zirconate, lead titanate, and lead magnesium niobate,an advantage is obtained in some cases, for example, in such a way thatthe coercive electric field and the piezoelectric characteristic can beadjusted.

It is desirable to avoid the addition of a material such as silica whichtends to form glass, because of the following reason. That is, thematerial such as silica tends to react with thepiezoelectric/electrostrictive material during the heat treatment forthe piezoelectric/electrostrictive layer. As a result, the compositionis varied, and the piezoelectric characteristic is deteriorated.

On the other hand, it is preferable that the pair of electrodes 28, 30of the piezoelectric/electrostrictive elements 24 a, 24 b are made ofmetal which is solid at room temperature and which is excellent inconductivity. For example, it is possible to use metal simple substanceor alloy of, for example, aluminum, titanium, chromium, iron, cobalt,nickel, copper, zinc, niobium, molybdenum, ruthenium, palladium,rhodium, silver, stannum, tantalum, tungsten, iridium, platinum, gold,and lead. It is also preferable to use a cermet material obtained bydispersing, in the metal described above, the same material as that ofthe piezoelectric/electrostrictive layer 26 and/or the thin platesections 16 a, 16 b.

The material for the electrodes 28, 30 of thepiezoelectric/electrostrictive elements 24 a, 24 b is selected anddetermined depending on the method for forming thepiezoelectric/electrostrictive layer 26. For example, when thepiezoelectric/electrostrictive layer 26 is formed by sintering on thefirst electrode 28 after the first electrode 28 is formed on the thinplate sections 16 a, 16 b, it is necessary for the first electrode 28 touse high melting point metal such as platinum, palladium,platinum-palladium alloy, and silver-palladium alloy which does notchange at the sintering temperature for thepiezoelectric/electrostrictive layer 26. However, the electrodeformation can be performed at a low temperature for the second electrode30 which is formed on the piezoelectric/electrostrictive layer 26 afterforming the piezoelectric/electrostrictive layer 26. Therefore, it ispossible for the second electrode 30 to use low melting point metal suchas aluminum, gold, and silver.

The thickness of the electrodes 28, 30 also serves as a factor toconsiderably decrease the displacement of thepiezoelectric/electrostrictive elements 24 a, 24 b. Therefore, it ispreferable, especially for the electrode formed after the sintering ofthe piezoelectric/electrostrictive layer 26, to use organic metal pastecapable of obtaining a dense and thinner film after the sintering, forexample, a material such as gold resinate paste, platinum resinatepaste, and silver resinate paste.

Next, explanation will be made with reference to FIGS. 16A to 26 for themethod for producing the piezoelectric/electrostrictive device 10according to the embodiment of the present invention.

Ceramics is preferably used for the constitutive material for each ofthe members of the piezoelectric/electrostrictive device 10 according tothe embodiment of the present invention. It is preferable that theconstitutive elements of the piezoelectric/electrostrictive device 10concerning the substrate 14 except for thepiezoelectric/electrostrictive elements 24 a, 24 b, i.e., the thin platesections 16 a, 16 b, the fixation section 22, and the movable section 20are produced by using the ceramic green sheet-laminating method.

On the other hand, it is preferable that thepiezoelectric/electrostrictive elements 24 a, 24 b as well as therespective terminals 32, 34 are produced by using the film formationmethod, for example, for the thin film and the thick film.

According to the ceramic green sheet-laminating method in which therespective members of the substrate 14 of thepiezoelectric/electrostrictive device 10 can be formed in an integratedmanner, the time-dependent change of state scarcely occurs at the joinedportions of the respective members. Therefore, this method provides thehigh reliability of the joined portion, and it is advantageous to ensurethe rigidity.

In the piezoelectric/electrostrictive device 10 according to thisembodiment, the boundary portion (joined portion) between the thin platesections 16 a, 16 b and the fixation section 22 and the boundary portion(joined portion) between the thin plate sections 16 a, 16 b and themovable section 20 function as supporting points for expressing thedisplacement. Therefore, the reliability of the joined portion is animportant point which dominates the characteristic of thepiezoelectric/electrostrictive device 10.

The production methods described below are excellent in reproducibilityand formability. Therefore, it is possible to obtain thepiezoelectric/electrostrictive device 10 having a predetermined shapewithin a short period of time with good reproducibility.

A first production method for the piezoelectric/electrostrictive device10 according to the embodiment of the present invention will bespecifically explained below. The laminate, which is obtained bylaminating the ceramic green sheets, is defined to be the ceramic greenlaminate 58 (see, for example, FIG. 16B). The integrated matter, whichis obtained by sintering the ceramic green laminate 58, is defined to bethe ceramic laminate 60 (see, for example, FIG. 17). The integratedmatter comprising the movable section 20, the thin plate sections 16 a,16 b, and the fixation section 22, which is obtained by cutting offunnecessary portions from the ceramic laminate 60, is defined to be theceramic substrate 14C (see FIG. 18).

In the first production method, the ceramic laminate 60 is finally cutinto chip units to produce a large number ofpiezoelectric/electrostrictive devices 10. However, in order to simplifythe explanation, description will be made principally for the case inwhich one individual of piezoelectric/electrostrictive device 10 isproduced.

At first, for example, a binder, a solvent, a dispersing agent, and aplasticizer are added and mixed with a ceramic powder such as zirconiato prepare a slurry. The slurry is subjected to a degassing treatment,and then a ceramic green sheet having a predetermined thickness isprepared in accordance with, for example, the reverse roll coater methodand the doctor blade method.

Subsequently, the ceramic green sheet is processed into those havingvarious shapes as shown in FIG. 16A in accordance with, for example, thepunching out based on the mold and the laser machining to obtain aplurality of ceramic green sheets 50A to 50D, 52A, 52B for forming thesubstrate.

The ceramic green sheets 50A to 50D, 52A, 52B include the plurality (forexample, four) of ceramic green sheets 50A to 50D each of which isformed with a window 54 for forming at least the hole 12 thereafter, andthe plurality (for example, two) of ceramic green sheets 52A, 52B to beformed into the thin plate sections 16 a, 16 b thereafter. In this case,those having the difference in sintering shrinkage speed and/orsintering shrinkage amount are used for the ceramic green sheets 50A to50D and the ceramic green sheets 52A, 52B respectively. Specifically,those used are exemplified such that the ceramic green sheets 50A to 50Dare sintered at fast timing as compared with the ceramic green sheets52A, 52B during the sintering of the ceramic green sheets, or thesintering shrinkage amount of the ceramic green sheets 50A to 50D issmaller than that of the ceramic green sheets 52A, 52B. The numbers ofceramic green sheets referred to above are not limited thereto but byway of example.

In this process, the denting amount of the thin plate sections 16 a, 16b after the sintering differs depending on the magnitude of thedifference in sintering shrinkage speed and/or the difference insintering shrinkage amount. Therefore, the ceramic green sheets 50A to50D and the ceramic green sheets 52A, 52B are selected so that thedifference in sintering shrinkage speed and/or the difference insintering shrinkage amount is given with which a desired denting amountis obtained.

When only the thin plate section 16 a or 16 b disposed on one side, ofthe pair of thin plate sections 16 a, 16 b is allowed to previously dentinwardly, it is preferable that the relationship for the ceramic greensheets described above is applied to any one of the ceramic green sheets52A, 52B.

After that, as shown in FIG. 16B, the ceramic green sheets 50A to 50D,52A, 52B are laminated and secured under pressure so that the ceramicgreen sheets 50A to 50D are interposed between the ceramic green sheets52A, 52B to form a ceramic green laminate 58.

It is necessary to bore a throughhole (not shown) allowing the window 54to communicate with the external space in the ceramic green laminate 58.This throughhole discharges from the inside of the ceramic greenlaminate 58 decomposed gases of binders and vapors of the remainingorganic solvents or the like generated during the sintering step of theceramic green laminate 58, so that cracking or unintended deformation,or the like of the thin plate section can be prevented.

Subsequently, as shown in FIG. 16C, the ceramic green laminate 58 issintered to obtain a ceramic laminate 60. In this process, the ceramicgreen sheets 50A to 50D are sintered at the timing faster than that ofthe ceramic green sheets 52A, 52B, and/or the sintering shrinkage amountof the ceramic green sheets 50A to 50D is made smaller than that of theceramic green sheets 52A, 52B. Therefore, the portions to be formed intothe thin plate sections thereafter, of the both first principal surfacesof the ceramic laminate 60 dent inward.

It is noted that there is no limitation for the number ofpressure-securing process or processes and the sequence for the purposeof the laminating and integration into one unit. These factors can beappropriately determined depending on the structure, for example, sothat the desired structure is obtained on the basis of, for example, theshape of the window 54 and the number of ceramic green sheets.

It is unnecessary that the shape of the window 54 is identical in allcases. The shape of the window 54 can be determined depending on thedesired function. There is also no limitation for the number of ceramicgreen sheets and the thickness of each of the ceramic green sheets.

In the pressure-securing process, it is possible to further improve thelaminating performance by applying the heat. The laminating performanceat the boundary of the ceramic green sheet can be improved by providingan auxiliary joining layer, for example, by applying and printing, ontothe ceramic green sheet, a paste or a slurry principally containing aceramic powder (it is preferable to use a composition which is the sameas or similar to that of the ceramics used for the ceramic green sheetin order to ensure the reliability), and a binder. When the ceramicgreen sheets 52A, 52B are thin, it is preferable to handle them with aplastic film, especially with a polyethylene terephthalate film coatedwith a releasing agent based on silicone on the surface.

Subsequently, as shown in FIG. 17, the piezoelectric/electrostrictiveelements 24 a, 24 b are formed respectively on the both surfaces of theceramic laminate 60, i.e., on the surfaces corresponding to the surfacesat which the ceramic green sheets 52A, 52B are laminated. Those usableas the method for forming the piezoelectric/electrostrictive elements 24a, 24 b include the thick film formation method such as the screenprinting method, the dipping method, the coating method, and theelectrophoresis method, and the thin film formation method such as theion beam method, the sputtering method, the vacuum vapor deposition, theion plating method, the chemical vapor deposition method (CVD), and theplating.

When the piezoelectric/electrostrictive elements 24 a, 24 b are formedby using the film formation method as described above, thepiezoelectric/electrostrictive elements 24 a, 24 b and the thin platesections 16 a, 16 b can be integrally joined and arranged without usingany adhesive. It is possible to ensure the reliability and thereproducibility, and it is easy to form the integration.

In this case, it is preferable that the piezoelectric/electrostrictiveelements 24 a, 24 b are formed by means of the thick film formationmethod, because of the following reason. That is, especially, when thepiezoelectric/electrostrictive layer 26 is formed by using the thickfilm formation method, the film can be formed by using, for example, apaste, a slurry, a suspension, an emulsion, or a sol containing a majorcomponent of particles or powder of piezoelectric ceramics having anaverage particle size of 0.01 to 5 μm, preferably 0.05 to 3 μm. It ispossible to obtain good piezoelectric/electrostrictive characteristicsby sintering the formed film.

The electrophoresis method is advantageous in that the film can beformed at a high density with a high shape accuracy. The screen printingmethod is advantageous to simplify the production step, because it ispossible to simultaneously perform the film formation and the patternformation.

Explanation will be specifically made for the formation of thepiezoelectric/electrostrictive elements 24 a, 24 b. At first, theceramic green laminate 58 is sintered and integrated into one unit at atemperature of 1200° C. to 1600° C. to obtain the ceramic laminate 60.After that, the first electrodes 28 are printed and sintered atpredetermined positions on the both surfaces of the ceramic laminate 60.Subsequently, the piezoelectric/electrostrictive layers 26 are printedand sintered. Further, the second electrodes 30 are printed and sinteredto form the piezoelectric/electrostrictive elements 24 a, 24 b. Afterthat, the terminals 32, 34 are printed and sintered in order toelectrically connect the respective electrodes 28, 30 to the drivingcircuit.

In this process, when the materials are selected so that the sinteringtemperature for each of the members is lowered in accordance with thestacking sequence, for example, when platinum (Pt) is used for the firstelectrode 28, lead zirconate titanate (PZT) is used for thepiezoelectric/electrostrictive layer 26, gold (Au) is used for thesecond electrode 30, and silver (Ag) is used for the terminals 32, 34,then the material, which has been already sintered beforehand, is notsintered again at a certain sintering stage. Thus, it is possible toavoid the occurrence of inconvenience such as peeling off andaggregation of the electrode material or the like.

When appropriate materials are selected, it is also possible tosuccessively print the respective members of thepiezoelectric/electrostrictive elements 24 a, 24 b and the terminals 32,34, followed by the sintering one time. Further, it is also possible toprovide, for example, the respective electrodes 30 at a low temperatureafter forming the piezoelectric/electrostrictive layers 26.

The sintering temperature of the constitutive film of thepiezoelectric/electrostrictive elements 24 a, 24 b is appropriatelydetermined depending on the material for constructing the same. However,the sintering temperature is generally 500° C. to 1500° C. The sinteringtemperature is preferably 1000° C. to 1400° C. for thepiezoelectric/electrostrictive layer 26. In this case, in order tocontrol the composition of the piezoelectric/electrostrictive layer 26,the sintering is preferably performed in the presence of an evaporationsource of the material of the piezoelectric/electrostrictive layer 26.

It is also preferable that the respective members of thepiezoelectric/electrostrictive elements 24 a, 24 b and the terminals 32,34 are formed in accordance with the thin film formation method such asthe sputtering method and the vapor deposition method. In this case, itis not necessarily indispensable to perform the heat treatment.

Subsequently, unnecessary portions are cut off from the ceramic laminate60 formed with the piezoelectric/electrostrictive elements 24 a, 24 b asdescribed above. The cutoff positions are located at side portions ofthe ceramic laminate 60, especially at portions at which the hole 12based on the window 54 is formed on the side surfaces of the ceramiclaminate 60 by means of the cutoff (see cutting lines C1 and C2). As aresult of the cutoff, as shown in FIG. 18, thepiezoelectric/electrostrictive device 10 according to the embodiment ofthe present invention is completed, in which thepiezoelectric/electrostrictive elements 24 a, 24 b are formed on theceramic substrate 14C wherein the pair of thin plate sections 16 a, 16 bare respectively bent In the directions to make mutual approach so thatthe inwardly convex configuration to the hole is given.

Those applicable as the cutoff method include the mechanical machiningsuch as the dicing machining, the wire saw machining and the slicingmachining as well as the electron beam machining and the laser machiningbased on the use of, for example, the YAG laser and the excimer laser.When the cutoff is performed, it is preferable that the heat treatmentis performed at 300 to 800° C. after the cutoff, because of thefollowing reason. That is, any defect such as microcrack tends to occurin the device as a result of the machining, while the defect can beremoved by means of the heat treatment described above, and thereliability is improved. Further, it is preferable to apply the agingtreatment by being left to stand for at least 10 hours at a temperatureof about 80° C. after the heat treatment, because of the followingreason. That is, when the aging treatment is performed, for example, thevarious stresses, which have been exerted during the production process,can be mitigated to contribute to the improvement in characteristic.

Next, a second production method will be explained with reference toFIGS. 19A to 19B. In the second production method, as shown in FIG. 19A,precursors 124 a, 124 b of the piezoelectric/electrostrictive elements24 a, 24 b are formed on both surfaces of the ceramic green laminate 58,i.e., on the respective surfaces of the ceramic green sheets 52A, 52B.

In this process, the formation is made while making the control suchthat the difference in thermal expansion is smaller in the thin platesections 16 a, 16 b, concerning the material for the portions to beformed into at least the thin plate sections 16 a, 16 b and the materialfor the precursors 124 a, 124 b of the piezoelectric/electrostrictiveelements 24 a, 24 b. Preferably, it is desirable to make the adjustmentand control so that the ratio of coefficient of thermal expansionbetween the materials (the ratio of the coefficient of thermal expansionof the precursors 124 a, 124 b of the piezoelectric/electrostrictiveelements 24 a, 24 b to the coefficient of thermal expansion of thematerial for constructing the thin plate sections 16 a, 16 b) is withina range of 1 to 10.

Accordingly, when the ceramic green laminate 58 and the precursors 124a, 124 b of the piezoelectric/electrostrictive elements 24 a, 24 b areco-fired to convert the ceramic green laminate 58 into the ceramiclaminate 60 as shown in FIG. 19B, the following arrangement isconsequently obtained. That is, the portions to be formed into the thinplate sections 16 a, 16 b thereafter of the ceramic laminate 60 inwardlydent, and the piezoelectric/electrostrictive elements 24 a, 24 b areformed on the portions to be formed into the thin plate sections 16 a,16 b, owing to the difference in thermal expansion at least between thematerial for the portions to be formed into the thin plate sections 16a, 16 b and the material for the precursors 124 a, 124 b of thepiezoelectric/electrostrictive elements 24 a, 24 b.

When the foregoing co-firing is performed, it is also preferable toperform the sintering of the ceramic green laminate 58 and for all ofthe constitutive films of the piezoelectric/electrostrictive elements 24a, 24 b. For example, other methods are available as follows. That is,the first electrode 28 and the ceramic green laminate 58 are co-fired.Alternatively, the other constitutive films except for the secondelectrode 30 and the ceramic green laminate 58 are co-fired.

In other words, the precursors 124 a, 124 b of thepiezoelectric/electrostrictive elements 24 a, 24 b refer to all of theconstitutive films of the piezoelectric/electrostrictive elements 24 a,24 b before the sintering, or the other constitutive films except forthe second electrode 30 of the piezoelectric/electrostrictive elements24 a, 24 b before the sintering.

The following method is available to co-fire thepiezoelectric/electrostrictive elements 24 a, 24 b and the ceramic greenlaminate 58. That is, precursors of the piezoelectric/electrostrictivelayers 26 are formed, for example, in accordance with the tape formationmethod based on the use of a slurry material. The precursors of thepiezoelectric/electrostrictive layers 26 before the sintering arelaminated on the surfaces of the ceramic green laminate 58, for example,by means of the thermal securing process under pressure, followed by theco-firing to simultaneously produce the movable section 20, the thinplate sections 16 a, 16 b, the piezoelectric/electrostrictive layers 26,and the fixation section 22. However, in this method, it is necessary toform the electrodes 28 on the surfaces of the ceramic green laminate 58and/or on the piezoelectric/electrostrictive layers 26 by using the filmformation method described above.

Another method is also available. That is, the electrodes 28, 30 and thepiezoelectric/electrostrictive layers 26, which are the respectiveconstitutive layers of the piezoelectric/electrostrictive elements 24 a,24 b, are formed by means of the screen printing on portions to befinally formed into at least the thin plate sections 16 a, 16 b of theceramic green laminate 58, followed by the co-firing.

When the piezoelectric/electrostrictive layers 26 and the ceramic greenlaminate 58 are co-fired, it is necessary to conform the sinteringconditions of the both. The piezoelectric/electrostrictive elements 24a, 24 b are not necessarily formed on the both surfaces of the ceramiclaminate 60 or the ceramic green laminate 58. It is of course allowableto form the piezoelectric/electrostrictive elements 24 a, 24 b on onlyone surface.

Subsequently, as shown in FIG. 19B, the ceramic laminate 60, which isformed with the piezoelectric/electrostrictive elements 24 a, 24 b, iscut along cutting lines C1 and C2 to cut off side portions of theceramic laminate 60. According to the cutoff, as shown in FIG. 18, thepiezoelectric/electrostrictive device 10 according to the embodiment ofthe present invention is completed.

Next, a third production method will be explained with reference toFIGS. 20A to 20B. In the above-described first production method, withrespect to the surface of the ceramic laminate 60 on which thepiezoelectric/electrostrictive elements 24 a, 24 b are formed, theportions to be formed into the thin plate sections 16 a, 16 b are dented(see FIG. 16C). In this third production method, as shown in FIG. 20A,the ceramic laminate 60 in which the surfaces to be formed into the thinplate sections 16 a, 16 b are made flat is used as the ceramic laminate60 in which the piezoelectric/electrostrictive elements 24 a, 24 b areformed, and the precursors 124 a, 124 b of thepiezoelectric/electrostrictive elements 24 a, 24 b are formed on thesurface of the ceramic laminate 60 according to the above-describedprocess, for example, the screen printing method.

Subsequently, as shown in FIG. 20B, the precursors 124 a, 124 b of thepiezoelectric/electrostrictive elements 24 a, 24 b are sintered andintegrated with the ceramic laminate 60. At this time, the respectivematerials are selected such that a ratio of coefficient of thermalexpansion between the portions to be formed into the thin plate sections16 a, 16 b of the ceramic laminate 60 and the precursors 124 a, 124 b ofthe piezoelectric/electrostrictive elements 24 a, 24 b (the ratio of thecoefficient of thermal expansion of the precursors 124 a, 124 b of thepiezoelectric/electrostrictive elements 24 a, 24 b to the coefficient ofthermal expansion of the material for constructing the thin platesections 16 a, 16 b) is within a range of from 0.05 to 2, whereby theceramic laminate 60 having a desired shape can be obtained at the sametime when the precursors 124 a, 124 b are sintered.

The precursors 124 a, 124 b as referred to herein means objects to besintered for forming any one of the pair of electrodes 28, 30 (or bothof electrodes 28, 30) constituting the piezoelectric/electrostrictiveelements 24 a, 24 b; and/or for forming thepiezoelectric/electrostrictive layer 26.

Subsequently, as shown in FIG. 20B, the ceramic laminate 60 on which thepiezoelectric/electrostrictive elements 24 a, 24 b are formed is cutalong cutting lines C1 and C2, thereby cutting off side portions of theceramic laminate 60. By this cutting, the piezoelectric/electrostrictivedevice according to the present invention is completed, as shown in FIG.18.

The embodiments of the first to third production methods described aboveare illustrative of the case in which the movable section 20, thefixation section 22, and the thin plate sections 16 a, 16 b areconstructed by the ceramic substrate 14C. Alternatively, each of theparts may be made of a metal material. Further alternatively, each ofthe parts may be made to provide a hybrid structure obtained bycombining those produced with materials of ceramics and metal. In thiscase, in order to join the metal materials to one another and/or jointhe ceramic and metal materials to one another, for example, it ispossible to use adhesion with organic resin or glass, brazing,soldering, eutectic bonding, or welding.

Explanation will be made with reference to FIGS. 21A to 27, for example,for production methods (fourth and fifth production methods) forpiezoelectric/electrostrictive devices (piezoelectric/electrostrictivedevices 10 j and 10 k according to tenth and eleventh modifiedembodiments) having the hybrid structure in which the movable section 20and the fixation section 22 are made of ceramics, and the thin platesections 16 a, 16 b are made of metal. The substrate containing metaland ceramics, which is produced by the fourth and fifth productionmethods, is referred to as the substrate 14D.

In the fourth production method, at first, as shown in FIG. 21A, aplurality (for example, four) of frame-shaped ceramic green sheets 50Ato 50D, each of which is formed with a window 54 for forming at leastthe hole 12 thereafter, are prepared.

After that, as shown in FIG. 21B, the ceramic green sheets 50A to 50Dare laminated and secured under pressure to form a ceramic greenlaminate 158 having no thin plate (having no portions to be formed intothe thin plate sections 16 a, 16 b thereafter). After that, as shown inFIG. 22A, the ceramic green laminate 158 having no thin plate issintered to obtain a ceramic laminate 160 having no thin plate. At thisstage, the ceramic laminate 160 having no thin plate (having no portionsto be formed into the thin plate sections 16 a, 16 b thereafter) isformed such that the hole 130 is formed by the windows 54.

Subsequently, as shown in FIG. 22B, the piezoelectric/electrostrictiveelements 24 a, 24 b, which are constructed as separate members, arerespectively bonded with an epoxy adhesive to the surfaces of metalplates 152A, 152B to serve as the thin plate sections. In this case,those used as the metal plates 152A, 152B are obtained by forming 154 bypreviously allowing the portions to be formed into the thin platesections 16 a, 16 b to dent in the certain direction, for example, bymeans of press working. The embodiment shown in FIG. 22B is illustrativeof the case in which parts of the metal plates 152A, 152B are allowed todent to give a concave configuration respectively. The separate membersof the piezoelectric/electrostrictive elements 24 a, 24 b can be formed,for example, in accordance with the ceramic green sheet-laminatingmethod. In this case, it is also preferable that the precursors 124 a,124 b of the piezoelectric/electrostrictive elements 24 a, 24 b areallowed to make dent by means of tooling or the like in the same manneras in the metal plates 152A, 152B described above.

Subsequently, the metal plates 152A, 152B are bonded to the ceramiclaminate 160 with the epoxy adhesive so that the ceramic laminate 160 isinterposed between the metal plates 152A, 152B and the hole 130 isclosed thereby to provide a hybrid laminate 162 (see FIG. 23).

Subsequently, as shown In FIG. 23, the hybrid laminate 162, which Isformed with the piezoelectric/electrostrictive elements 24 a, 24 b, iscut along cutting lines C1 and C2 to thereby cut off side portions ofthe hybrid laminate 162.

As a result of the cutoff, as shown in FIG. 24, thepiezoelectric/electrostrictive device 10 j according to the tenthmodified embodiment is completed, in which thepiezoelectric/electrostrictive elements 24 a, 24 b are formed on thesubstrate 14D wherein the thin plate sections 16 a, 16 b constructed bythe metal plates 152A, 152B are previously bent in the directions tomake approach to each other to give the convex configuration toward thehole 12.

On the other hand, in the fifth production method, at first, in the samemanner as in the fourth production method described above, a plurality(for example, four) of frame-shaped ceramic green sheets 50A to 50D,each of which is formed with a window 54 for forming at least the hole12 thereafter, are prepared. The ceramic green sheets 50A to 50D arelaminated and secured under pressure to form a ceramic green laminate158 having no thin plate (see FIGS. 21A, 21B).

Subsequently, the ceramic green laminate 158 having,no thin plate issintered to obtain a ceramic laminate 160 as shown in FIG. 25A. At thisstage, the ceramic laminate 160 having no thin plate is formed such thatthe hole 130 is formed by the windows 54.

Subsequently, as shown in FIG. 25B, the metal plates 152A, 152B arebonded to the ceramic laminate 160 having no thin plate with an epoxyadhesive so that the ceramic laminate 160 having no thin plate isinterposed between the metal plates 152A, 152B and the hole 130 isclosed thereby to provide a hybrid laminate 162. Also in this case,those used for the metal plates 152A, 152B are obtained by previouslyallowing the portions to be formed into the thin plate sections 16 a, 16b thereafter to dent in the certain directions by means of press workingor the like.

Further, in order to apply a sufficient force for bonding duringlaminating the piezoelectric/electrostrictive elements 24 a, 24 b on thesurfaces of the adhered metal plates 152A, 152B, a filler material 164is filled in the hole 130, if desired, as shown in FIG. 25A.

It is necessary to finally remove the filler material 164. Therefore, itis preferable to use a hard material which is easily dissolved in asolvent or the like. The material includes, for example, organic resin,wax, and brazing filler material. It is also possible to adopt amaterial obtained by mixing ceramic powder as a filler with organicresin such as acrylic.

Subsequently, as shown in FIG. 26, the piezoelectric/electrostrictiveelements 24 a, 24 b, which are constructed as separate members, arebonded with an epoxy adhesive to the surfaces of the metal plates 152A,152B of the hybrid laminate 162. The separate members of thepiezoelectric/electrostrictive elements 24 a, 24 b can be formed, forexample, in accordance with the ceramic green sheet-laminating method.

Subsequently, the hybrid laminate 162, which is formed with thepiezoelectric/electrostrictive elements 24 a, 24 b, is cut along cuttinglines C1 and C2 to thereby cut off side portions of the hybrid laminate162. As a result of the cutoff, as shown in FIG. 27, thepiezoelectric/electrostrictive device 10 k according to the eleventhmodified embodiment is obtained, in which thepiezoelectric/electrostrictive elements 24 a, 24 b are formed on thesubstrate 14D wherein the thin plate sections 16 a, 16 b constructed bythe metal plates 152A, 152B are previously bent in the directions tomake mutual approach to give the convex configuration toward the hole12.

When all of the substrate section is made of metal, for example, theportions corresponding to the ceramic laminate 160 shown in FIG. 22A areformed by means of molding. Further, thin metal materials may be stackedto form the substrate section in accordance with the cladding method.

The various piezoelectric/electrostrictive devices described above areillustrative of the case in which the central portions of the thin platesections 16 a, 16 b dent inwardly. However, as in apiezoelectric/electrostrictive device 10 m according to a twelfthmodified embodiment shown in FIG. 28, it is also preferable thatportions other than the central portions of the thin plate sections 16a, 16 b may dent inwardly. This structure can be formed with ease, forexample, by means of press working when the thin plate sections 16 a, 16b are made of metal. Alternatively, the structure can be similarlyformed such that the thin plate sections 16 a, 16 b are formed to beflat beforehand, and then they are pressed from the outside toward ofthe hole 12.

The embodiments described above are illustrative of the case in whichboth of the pair of thin plate sections 16 a, 16 b are bent inwardly,and the piezoelectric/electrostrictive elements 24 a, 24 b are formed onboth of the thin plate sections 16 a, 16 b. Alternatively, as in apiezoelectric/electrostrictive device 10 n according to a thirteenthmodified embodiment shown in FIG. 29, for example, it is also preferablethat only the first thin plate section 16 a is bent inwardly, and thepiezoelectric/electrostrictive elements 24 a, 24 b are formed on both ofthe thin plate sections 16 a, 16 b respectively. Alternatively, as in apiezoelectric/electrostrictive device 10 p according to a fourteenthmodified embodiment shown in FIG. 30, it is also preferable that onlythe first thin plate section 16 a is bent inwardly, and thepiezoelectric/electrostrictive element 24 a is formed on the first thinplate section 16 a. Further alternatively, as in apiezoelectric/electrostrictive device 10 q according to a fifteenthmodified embodiment shown in FIG. 31, it is also preferable that both ofthe pair of thin plate sections 16 a, 16 b are bent inwardly, and thepiezoelectric/electrostrictive element 24 a is formed on the first thinplate section 16 a of them.

The piezoelectric/electrostrictive devices 10 p, 10 q, in which thepiezoelectric/electrostrictive element 24 a is formed on only one thinplate section 16 a of the pair of mutually opposing thin plate sections16 a, 16 b as described above, make it possible to decrease the rigidityof the thin plate section 16 b on which thepiezoelectric/electrostrictive element 24 b is not formed.

As a result, comparison may be made concerning the magnitude of thedisplacement obtained by operating one piezoelectric/electrostrictiveelement 24 a, between the piezoelectric/electrostrictive device (forexample, piezoelectric/electrostrictive device 10) in which thepiezoelectric/electrostrictive elements 24 a, 24 b are formed on theboth sides and the piezoelectric/electrostrictive device (10 p or 10 q)in which the piezoelectric/electrostrictive element 24 a is formed ononly one side. The piezoelectric/electrostrictive device (10 p or 10 q),in which the piezoelectric/electrostrictive element 24 a is formed ononly one side, has such a feature that it is possible to obtain thegreater displacement, owing to the effect that the rigidity of the thinplate section 16 b disposed on the opposed side is low.

The piezoelectric/electrostrictive device described above can beutilized as the active device including, for example, varioustransducers, various actuators, frequency region functional parts(filters), transformers, vibrators, resonators, oscillators, anddiscriminators for the communication and the power generation, as wellas the sensor element for various sensors including, for example,ultrasonic sensors, acceleration sensors, angular velocity sensors,shock sensors, and mass sensors. Especially, thepiezoelectric/electrostrictive device described above can be preferablyutilized for various actuators to be used for the mechanism foradjusting the displacement and the positioning and for adjusting theangle for various precision parts such as those of optical instrumentsand precision mechanical equipments.

It is a matter of course that the piezoelectric/electrostrictive deviceand the method for producing the same according to the present inventionare not limited to the embodiments described above, which may beembodied in other various forms without deviating from the gist oressential characteristics of the present invention.

What is claimed is:
 1. A piezoelectric/electrostrictive devicecomprising: a pair of mutually opposing thin plate sections, a movablesection, and a fixation section for supporting said thin plate sectionsand said movable section; one or more piezoelectric/electrostrictiveelements arranged on at least one thin plate section of said pair ofthin plate sections; and a hole formed by both inner walls of-said pairof thin plate sections, an inner wall of said movable section, and aninner wall of said fixation section, wherein: at least one thin platesection of said pair of thin plate sections is previously bent in adirection to make mutual approach.
 2. A piezoelectric/electrostrictivedevice comprising: a pair of mutually opposing thin plate sections, amovable section, and a fixation section for supporting said thin platesections and said movable section; one or morepiezoelectric/electrostrictive elements arranged on at least one thinplate section of said pair of thin plate sections; and a hole formed byboth inner walls of said pair of thin plate sections, an inner wall ofsaid movable section, and an inner wall of said fixation section,wherein: said pair of thin plate sections are previously bent indirections to make mutual approach.
 3. Thepiezoelectric/electrostrictive device according to claim 1, wherein atleast one thin plate section of said pair of thin plate sections ispreviously bent inwardly toward said hole in a convex configuration. 4.The piezoelectric/electrostrictive device according to claim 1, wherein0<δ≦0.13 L is satisfied provided that a bent amount of said thin platesection is δ, and a distance between said inner walls of said movablesection and said fixation section is L.
 5. Thepiezoelectric/electrostrictive device according to claim 1, wherein saidthin plate section, said movable section, and said fixation section arecomposed of a ceramic substrate integrated into one unit bysimultaneously sintering a ceramic green laminate and cutting offunnecessary portions.
 6. The piezoelectric/electrostrictive deviceaccording to claim 5, wherein said piezoelectric/electrostrictiveelement has a film-shaped configuration, and at least any one of a pairof electrodes and/or a piezoelectric/electrostrictive layer isintegrated with said ceramic substrate by means of sintering.
 7. Thepiezoelectric/electrostrictive device according to claim 1, wherein saidpiezoelectric/electrostrictive element has apiezoelectric/electrostrictive layer and a pair of electrodes formed onsaid piezoelectric/electrostrictive layer.
 8. Thepiezoelectric/electrostrictive device according to claim 1, wherein saidpiezoelectric/electrostrictive element has apiezoelectric/electrostrictive layer and a pair of electrodes formed onboth sides of said piezoelectric/electrostrictive layer, and oneelectrode of said pair of electrodes is formed on at least said thinplate section.
 9. The piezoelectric/electrostrictive device according toclaim 7, wherein said piezoelectric/electrostrictive element isconstructed in a stacked form comprising a plurality of saidpiezoelectric/electrostrictive layers and said electrodes.
 10. Thepiezoelectric/electrostrictive device according to claim 1, wherein saidhole is filled with a gel material.